Selective surface exposure, cleans and conditioning of the germanium film in a Ge photodetector

ABSTRACT

A method of protecting a sensitive layer from harsh chemistries. The method includes forming a first sensitive layer, forming a second layer upon the first layer, then forming a third layer over the second layer. The third layer is utilized as a mask during patterning of the second layer. During patterning, however, the second layer is only partially etched, thus leaving a buffer layer overlying the first layer. The third layer is completely removed while the buffer layer protects the first layer from the harsh chemicals that are utilized to remove the third layer. Then, the buffer layer is carefully removed down to the surface of the first layer.

This is a Divisional application of Ser. No. 10/607,955 filed Jun. 26,2003, which is presently pending.

FIELD

The present invention relates generally to the field of semiconductortechnology and, more specifically, to etching and cleaning sensitivematerials.

BACKGROUND

In the semiconductor fabrication arts, it is often necessary to fashion(etch, pattern, etc.) layers of differing materials according to a givendesign to create electronic devices, interconnections, or otherstructures in an integrated circuit. Photolithography is commonly usedto create patterns within the layers of an integrated circuit. FIG.1A-1C illustrates a typical photolithography process. As shown in FIG.1A, a photoresist material 1 is deposited atop a first layer 2 that isto be etched. Layer 2 may overlay any number of other layers, forexample, layer 3. According to well known masking, exposing, anddeveloping techniques, the photoresist material 1 is patterned to createan opening 4. Layer 2 may then be etched through the opening, such as bya reactive ion etch (RIE), shown in FIG. 1B. The RIE utilizes an etchant5 that etches the material of layer 2, more selectively than thephotoresist material 1. Hence, the photoresist material 1 holds its formduring the etch and a cavity 8 can be formed into layer 2 according tothe patterned opening 4. At the same time, the etchant 5 that etcheslayer 2, does so at a much higher rate than it etches the material ofunderlying layer 3, hence the underlying layer 3 acts as an etch stop.

Typically, after forming the cavity 8 in layer 2, the photoresistmaterial 1 needs to be removed to enable further processing of layer 2or layer 3. Consequently, as shown in FIG. 1C, the photoresist material1 may be removed according to the similar etching methods, such as RIE,O₂ high pressure ashing, and/or well-known wet cleaning techniques.Layer 2 and layer 3 are typically durable semiconductive, insulative, orconductive materials that are conventionally used in integratedcircuits, so that during the removal of the photoresist material 1,layers 2 and 3 do not typically have to be protected when thephotoresist material 1 is being removed. Additionally, the oxygen plasmadamage from RIE is very minimal on these types of materials. Examples ofdurable materials may include silicon, silicon oxide, silicon nitride,polysilicon, and other materials that are durable to chemistries thatremove conventional photoresist materials. As a result, the photoresistmaterial 1, has, until now, been removed without fear of damagingunderlying thin films or structures.

However, modern technologies are rapidly exploring the use of new anddifferent materials that have not typically been used in the formationof integrated circuits. These new and different materials may includematerials that are sensitive to chemistries that, until now, have notpresented problems. For example, germanium has been proposed to replacesilicon as a semiconductor of choice for many fabrication processes thatheretofore have used silicon. Germanium, however, tends to be verysensitive to certain chemistries, for example, the dry and wetchemistries utilized to remove photoresist materials. Consequently,previous methods of removing certain materials, such as photoresist,require new and unique techniques in order to maintain the integrity ofnew and different materials, such as germanium.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present invention are illustrated by way of exampleand should not be limited by the figures of the accompanying drawings inwhich like references indicate similar elements and in which:

FIG. 1A-1C illustrates a typical photolithography process;

FIG. 2A-2D illustrate a method according to one embodiment of theinvention, of removing a layer of patterning material without damagingan underlying sensitive material;

FIG. 3A-3C illustrate a method, according to one embodiment of theinvention, of conditioning the top surface of the sensitive layer afterthe patterning material has been removed; and

FIG. 4A-4D illustrate a method according to one embodiment of theinvention, of removing a photoresist layer without damaging anunderlying sensitive germanium layer; and

FIG. 5A-5C a method, according to one embodiment of the invention, ofconditioning the top surface of the sensitive germanium layer after thephotoresist layer has been removed.

DETAILED DESCRIPTION

Described herein is a method of etching and cleaning a sensitive layerin the formation of semiconductive structures, integrated circuitry, andother generally related electronic devices. In the following descriptionnumerous specific details are set forth. One of ordinary skill in theart, however, will appreciate that these specific details are notnecessary to practice embodiments of the invention. While certainexemplary embodiments of the invention are described and shown in theaccompanying drawings, it is to be understood that such embodiments aremerely illustrative and not restrictive of the current invention, andthat this invention is not restricted to the specific constructions andarrangements shown and described since modifications may occur to thoseordinarily skilled in the art. In other instances well knownsemiconductor fabrication processes, techniques, materials, equipment,etc., have not been set forth in particular detail in order to notunnecessarily obscure embodiments of the present invention.

Described herein is a method of protecting a sensitive layer from harshchemistries. In brief, the method includes forming a first sensitivelayer, forming a second layer upon the first layer, then forming a thirdlayer over the second layer. The third layer is utilized as a maskduring patterning of the second layer. During patterning, however, thesecond layer is only partially etched, thus leaving a buffer layeroverlying the first layer. The third layer is completely removed whilethe buffer layer protects the first layer from the harsh chemicals thatare utilized to remove the third layer. Then, the thinned portion of thebuffer layer is carefully removed down to the surface of the firstlayer.

FIG. 2A-2D illustrate a method according to one embodiment of theinvention, of removing a layer of patterning material without damagingan underlying sensitive material. Referring to FIG. 2A, the methodbegins with forming a first layer 202 over a substrate 200, forming asecond layer 204 over the first layer 202 and forming a third layer 206over the second layer 204. The third layer 206 is patterned to have anopening 208 therein. The pattern of the opening 208 will subsequently betransferred to the underlying second layer 204.

The first layer 202 comprises a very sensitive semiconductor materialthat is susceptive to damage from harsh chemistries (“first chemistry”)utilized during the patterning and removal of the third layer 206. Theterm “sensitive” means that the material composition of the first layer202 is easily etchable, removable, corruptible, or in other words, willundergo a severe material alteration if exposed directly to chemicalcompounds and/or solutions that comprise the first chemistry. Hence, thematerial of the first layer 202 and the chemical composition of thefirst chemistry can vary depending on the process. For example, in theformation of a semiconductor photodector device, one example of asensitive material may include germanium, which is utilized to form theoptical layer of the photodector. In other examples, such as in theformation of some transistors, sensitive materials may include III-Vsemiconductor compounds, such as gallium arsenide, aluminum nitride, orindium antiminide.

Still referring to FIG. 2A, the second layer 204, formed over the firstlayer 202, is not sensitive to the first chemistry previously described.The second layer 204 may be a nitride, an oxide, an oxynitride, or anyother material that is formed over the first, sensitive layer. Forexample, in one embodiment of the invention, the second layer 204 may bean insulating layer to insulate the first layer 202 from other materialswithin an integrated circuit. In another embodiment, the second layer204 may be a conductive or semiconductive material that will be utilizedin conjunction with the first layer 202 to form an active device, suchas an electrode of an electronic device. In other embodiments of theinvention, the second layer 204 may also include multiple layers ofdifferent materials that overlie the first, sensitive layer. Forexample, the second layer 204 may include a nitride overlying a padoxide. The second layer 204 may alternatively comprise anoxide/nitride/oxide composite. Hence, the actual composition of thematerial of the second layer 204 may vary. However, the second layer 204should comprise at least one material that is not sensitive to the harshchemicals of the first chemistry that will be utilized in thepatterning, and removal, of an overlying third layer 206, such as aphotoresist layer 206. For simplicity of disclosure, the second layer204 may be referred to herein as a “non-sensitive” layer, that “directlyoverlies” the sensitive layer, although one ordinarily skilled in theart may recognize that the second layer 204 may comprise more than onematerial or layers of materials.

The thickness of the second layer 204 may vary depending on the desiredprocess. However, in one embodiment of the invention, the second layer204 should be formed thick enough to protect the first layer 202 fromthe harsh, first chemistry. In other words, the second layer 204 shouldbe formed to a thickness that will withstand dry or wet etching of thesecond layer 204, when an overlying third layer 206 is being patterned,cleaned, or otherwise processed.

Still referring to FIG. 2A, the third layer 206 is formed directly ontop of the second layer 204. The third layer 206 is removable by thefirst, “harsh” chemistry. In one embodiment of the invention, thirdlayer 206 may be a photoresist material, or other type of material, usedto protect portions of the second layer 204 from being etched during aphotolithography process. In another embodiment of the invention, thethird layer 206 may instead be a hardmask material.

As described above, the third layer 206 is formed to have an opening208. The opening 208 is formed according to a designed width. In oneembodiment of the invention, a typical photolithography process mayinclude the well-known techniques of masking, exposing, and developingthe third layer 206 to form the opening 208. The pattern of the opening208 will subsequently be transferred to the underlying second layer 204.

Next, as shown in FIG. 2B, the method continues with substantiallyetching the thickness of the second layer 204 through the opening 208,but leaving a thin, unetched portion of the second layer 204 on thefirst layer 202. A substantial portion of the second layer 204'sthickness is removed in a substantially vertical fashion, to form ahole, or via 210, inside the second layer 204 having sidewalls 215 and abottom 216. The buffer layer 212, between the bottom 216 of the via 210and the top surface 218 of the first layer 202, is approximately 10% to25% of the original thickness of the second layer 204, and may herein betermed a “buffer layer” 212, since it will function as a buffer betweenthe bottom 216 of the via 210 and the top surface 218 of the first layer202, during the subsequent removal of the third layer 206. The formationof the via 210 may be accomplished by performing a timed dry etch of thesecond layer 204 through the opening 208. The timed etch is calculatedto remove approximately 75%-90% of the second layer 204. Dry etchingtechniques are well known in the art and may include such techniques asplasma etching, or reactive ion etching, which may utilize ions 211 of asecond chemistry that etches the second layer 204, but that does notsubstantially etch the third layer 206.

Next, as shown in FIG. 2C, the method continues with removing the thirdlayer 206 using the previously mentioned first chemistry. During theremoval of the third layer 206, the buffer layer 212 protects the firstlayer 202 from the first chemistry. If not for the buffer layer 212, thefirst layer 202 would be damaged by the harsh, first chemistry. However,because the buffer layer 212 is in place, the first layer 202 is sparedfrom the potential damage that would occur from the first chemistry.During the removal of the third layer 206, the buffer layer 212 mayundergo a partial etching. Hence, the thickness of the buffer layer 212should be thick enough to withstand partial etching, yet still have asubstantial portion of mass to still protect the first layer 202throughout the entire time that the third layer 206 is being removed,including any wet cleaning/ashing procedures.

Next, as shown in FIG. 2D, after the third layer 206 has been removedand cleaned, the method continues with removing the buffer layer 212with a chemistry to which the first layer 202 is not significantlysensitive. As a result, the first layer 202 can maintain itssubstantially planar shape, as originally formed. In one embodiment ofthe invention, the buffer layer 212 may be removed by the same chemistry(i.e., the second chemistry) previously used to etch the second layer204, as described above in conjunction with FIG. 2B. In addition tousing the second chemistry to which the first layer 202 is notsignificantly sensitive, the removal of the buffer layer 212 may beperformed very slowly, in a very controlled fashion, to better controlthe removal of the buffer layer 212 and ensure that the top surface 218of the first layer 202 is not damaged.

Additionally, a wet chemistry may be employed to clean any remainingresidue of the second layer 204. To minimize the impact of the wetcleaning chemistry on the first layer 202 the wet clean may be performedat room temperature, in very dilute concentrations, and for very briefperiods of time. Consequently, the via 210 is extended entirely throughthe second layer 204, to the top surface 218 of the first layer 202, yetthe top surface 218 of the first layer 202 remains substantially planar,as originally formed.

According to other embodiments of the invention, as shown in FIG. 3A-3C,after the via 210 has been formed completely through the second layer204, the method may further include conditioning the top surface 218 ofthe first layer 202 with a third, or “conditioning” chemistry. Theconditioning chemistry may cause the top surface 218 of the first layer202 to have primarily the same atomic termini.

FIG. 3A illustrates an enlarged view of the top surface 218 of the firstlayer 202. The sidewalls 215 of the via 210 are shown for context. Afterthe via 210 has been formed, the top surface 218 of the first layer 202may consist of various types of atomic termini. For reference, thesetypes of termini are shown in FIG. 3A-3C as either one of two types(type A or type B), however one skilled in the art may recognize thatmore than two types of termini may exist depending on how the firstlayer 202 was formed and also depending on the environment and/orchemicals that the top surface 218 of the first layer 202 had beenexposed to at any point during its formation, or during subsequentprocessing, such as during the formation and patterning of the overlyingsecond layer 204. The two types of atomic termini represent molecularendings that are attached, by molecular bonds, to the material of thefirst layer 202, represented by a molecular type C, and may be in anon-uniform pattern, as shown in FIG. 3A.

It would be desirable, however, in some circumstances, to have the topsurface 218 comprise a single atomic termini (i.e., either type A ortype B) depending on the composition of the material that will besubsequently formed atop the top surface 218. For example, certainmaterials may bond better to atoms of either type A or type B. Hence,for example, if a material is formed atop the top surface 218 of thefirst layer 202 that would bond better to a uniform layer of type Aatoms, it would be advantageous to apply a conditioning chemical to thetop of surface to make the surface comprise atoms that are primarily oftype A atoms.

Therefore, referring to FIG. 3B, in one embodiment of the invention, aconditioning solution 220 may be applied to the top surface 218 of thefirst layer 202 that causes the atomic termini to be converted primarilyto type A atoms. In a like manner, as shown in FIG. 3C, if atomictermini of type B atoms are desired, a different conditioning solution222 may be applied to the surface of the first layer 202 that causes theatomic termini to be converted primarily to type B atoms.

FIG. 4A-4D illustrate a method according to one embodiment of theinvention, of removing a photoresist layer without damaging anunderlying sensitive germanium layer. Referring first to FIG. 4A, agermanium layer 202 is formed on substrate 200. Above the germaniumlayer 202 is formed a nitride layer 204 and an oxide layer 502. Abovethe oxide layer 502 is formed a photoresist layer 206. An opening 208 isformed into the photoresist layer 206 by well-known masking, exposingand developing techniques. The germanium layer 202 is a material that issensitive to a harsh “photoresist-removal” chemistry (corresponding tothe “first chemistry” described in conjuction with FIG. 2A-2D above).The photoresist-removal chemistry is to remove the photoresist layer 206in a subsequent process, as described in conjunction with FIG. 4C below.The term “sensitive” means that the germanium layer 202 is easilyetchable, removable, corruptible, or in other words, will undergo asevere material alteration if exposed directly to chemical compoundsand/or solutions that comprise the photoresist-removal chemistry.Examples of the harsh photoresist-removal chemistry may include, but arenot limited to, well known O2 plasma etching and “Pirahna” ash(i.e., >80% sulfuric acid mixture) including oxidizing agents (i.e.,1-20% nitric acid or hydrogen peroxide).

In one embodiment, the germanium layer 202 may be 500 nm thick, thenitride layer 204 may be 100 nm thick, the oxide layer 502 may be 500 nmthick, and the photoresist layer 206 may be 500 nm thick, however thesethicknesses may vary slightly depending on the process. Nevertheless,since the nitride layer 204 directly overlies the sensitive germaniumlayer 202, the nitride layer 204 should be formed thick enough toprotect the germanium layer 202 from the harsh, photoresist-removalchemistry that will be subsequently utilized.

Still referring to FIG. 4A, the oxide layer 502 is formed directly ontop of the nitride layer 204. The oxide layer 502 can act as aninterlayer dielectric in a device with metalization or as opticalcladding for a waveguide.

Still referring to FIG. 4A, the photoresist layer 206 is formed toprotect portions of the oxide layer 502 and nitride layer 204 from beingetched during a photolithography process. Photolithography processes arewell known in the art and may include the steps including (1)positioning a patterned hardmask above the photoresist layer 206 withthe hardmask having a pattern, (2) directing electromagnetic energythrough the pattern of the hardmask so that the photoresist material isexposed, then, once exposed, (3) developing the photoresist material tocause the exposed photoresist material to dissolve, hence forming theopening 208.

Next, as shown in FIG. 4B, the method continues with etching the oxidelayer 502 and the nitride layer 204 directly through the opening 208, ina vertical fashion, such as with a reactive ion etch process. Reactiveion etching (RIE), an example of plasma etching, is a well knownprocedure that includes forming a plasma, within a reactive chamber, byigniting a gas having a particular chemistry, to form ions 211comprising the particular chemistry. The ions 211 are then forcedtowards the water substrate, by the sheath electric field, causingetching of the surfaces that are exposed to the forceful ions 211.Depending on the particular chemistry, however, different surfaces areetched at different rates. As shown in FIG. 4B, ions 211 are formed of achemistry that will remove either the oxide layer 502, the nitride layer204, or both. Typically, however, the oxide layer 502 and the nitridelayer 204 are etched utilizing two different etches with two differentchemistries. For example, in one embodiment of the invention, the oxidelayer 502 may be etched utilizing an oxide-etch chemistry (i.e.,CO/C₄F₈/O₂/Ar) selective to the nitride layer, while the nitride layer204 may be etched utilizing a nitride-etch chemistry (CH₂F₂/O₂/Ar). Incomparison to the method described in conjunction with FIGS. 2A-2Dabove, the oxide layer 502 and the nitride layer 204 may correspond tothe “second layer” 204.

Still referring to FIG. 4B, the oxide layer 502 is completely etchedaccording to the pattern of the opening 208 in the photoresist layer206. Then, the nitride layer 204 is etched, also according to thepattern of the opening 208. However, the nitride layer 204 is etchedaccording to a timed etch so that a thin portion of the nitride layer204, or “buffer layer” 212 remains unetched. Thus, a hole, or via 210,is formed having sidewalls 215 and a bottom 216. The buffer layer 212has a thickness extending between the bottom 216 of the via 210 and thetop surface 218 of the germanium layer 202. The buffer layer 212 is tofunction as a buffer between the bottom 216 of the via 210 and the topsurface 218 of the germanium layer 202, during the subsequent removal ofthe photoresist layer 206. The buffer layer 212 shown in FIG. 4B maycorrespond to the buffer layer 212 described in conjunction with FIGS.2A-2D above.

The timed etch is calculated to remove approximately 75%-90% of thenitride layer 204, hence causing the buffer layer 212 to beapproximately 10% to 25% of the original thickness of the nitride layer204. The thickness of the buffer layer 212 should not be less than about10% because of thickness non-uniformities that may result when formingthe buffer layer 212. In other words, because the buffer layer 212 maynot have a uniform thickness, to ensure that it protects the underlyinggermanium layer 202 from the harsh photoresist-removal chemistry, it isadvantageous to time the etch so that, at most, about 90% of the nitridelayer 204's original thickness is etched.

Likewise, the thickness of the buffer layer 212 should not be more thanabout 25% of the original thickness of the nitride layer 204 so that thebuffer layer 212 can subsequently be removed without too much effort.More specifically, as shown in conjunction with FIG. 4D below, thebuffer layer 212 eventually must be removed. To minimize damage to thegermanium layer 202 below, however, the buffer layer 212 should beremoved cautiously, with a slower etch rate, by utilizing either a moredilute chemistry or by etching more slowly. Thus, by limiting thethickness of the buffer layer 212 to at most about 25% of the originalthickness of the nitride layer 204, the buffer layer 212 can be removedslowly, yet still not take an excessively long time.

Next, as shown in FIG. 4C, the method continues with removing thephotoresist layer 206 using the previously mentioned photoresist-removalchemistry. Examples of the harsh photoresist-removal chemistry mayinclude, but are not limited to, well known O₂ plasma etching and“Pirahna” ash (i.e., >80% sulfuric acid mixture) including oxidizingagents (i.e., 1-20% nitric acid or hydrogen peroxide).

During the removal of the photoresist layer 206, the buffer layer 212protects the germanium layer 202 from the photoresist-removal chemistry.If not for the buffer layer 212, the germanium layer 202 would bedamaged by the harsh, photoresist-removal chemistry. However, becausethe buffer layer 212 is in place, the germanium layer 202 is spared fromthe potential damage that would occur from the photoresist-removalchemistry. In one embodiment of the invention, the photoresist-removalchemistry may be formulated to be selective to the nitride layer 204.Nonetheless, during the removal of the photoresist layer 206, the bufferlayer 212 may still undergo some partial etching from thephotoresist-removal chemistry. Hence, the thickness of the buffer layer212 should be thick enough to withstand partial etching, yet still havea substantial portion of mass to still protect the germanium layer 202throughout the entire time that the photoresist layer 206 is beingremoved, including any wet cleaning/ashing procedures. Therefore,because of partial etching that may occur from the photoresist-removalchemistry, it is advantageous to limit the minimum thickness of thebuffer layer 212 to no less than about 10% of the original thickness ofthe nitride layer. If, however, 10% of the original thickness of thenitride layer would not be sufficient to maintain an integral bufferlayer 212, the buffer layer 212 should consequently be formed thickerthan 10%.

Next, as shown in FIG. 4D, after the photoresist layer 206 has beenremoved and cleaned, the method continues with removing the buffer layer212 with a chemistry to which the germanium layer 202 is notsignificantly sensitive. As a result, the germanium layer 202 canmaintain its substantially planar shape, as originally formed. In oneembodiment of the invention, the buffer layer 212 may be removed by thesame nitride-etch chemistry previously used to etch the nitride layer204, as described above in conjunction with FIG. 4B. In addition tousing the nitride-etch chemistry, to which the germanium layer 202 isnot significantly sensitive, the removal of the buffer layer 212 may beperformed very slowly, in a very controlled fashion, to better controlthe removal of the buffer layer 212 and ensure that the top surface 218of the germanium layer 202 is not damaged. Hence, removal of the bufferlayer 212 may include performing a reactive ion etch at a lower energythat is approximately 50% lower than the RIE of FIG. 4B, and/orperforming an etch with a weaker nitride-etch chemistry that isapproximately 50% more dilute than that used in conjunction with FIG.4B.

Additionally, a wet chemistry may be employed to clean any remainingresidue of the nitride layer 204. To minimize the impact of the wetcleaning chemistry on the germanium layer 202 the wet clean may beperformed at room temperature, in very dilute concentrations, and forvery brief periods of time. Consequently, the via 210 is extendedentirely through the nitride layer 204, to the top surface 218 of thegermanium layer 202, yet the top surface 218 of the germanium layer 202remains substantially planar, as originally formed. It is highlyadvantageous for the top surface 218 of the germanium layer 202 to haveorthogonality, or in other words, planarity, to ensure the properfunctioning of the photodector device.

Still referring to FIG. 4D, it should be noted that during the removalof the buffer layer 212, without the presence of the photoresist layer206, the nitride-etch chemistry may cause the top surface 504 of theoxide layer 502 to undergo some slight etching. For example, given thenitride-etch and oxide-etch chemistries above, a selectivity to theoxide layer 502 may be about 7:2. Thus, the loss to the oxide layer 502may be approximately 3%-7% (i.e., (10%-25% nitride thickness)×(2/7))during the nitride buffer layer 212 etch. Therefore, referringmomentarily back to FIG. 5A, when the oxide layer 502 is formed,according to one embodiment of the invention, it may be formed thickerthan necessary to compensate for the loss during the etch of the bufferlayer 212, or more specifically, about 3%-7% thicker than necessarygiven a 7:2 selectivity. More generally, for a selectivity ofX_(nitride):Y_(oxide) the oxide layer 502 may be formed thicker thanintended to an additional degree of Y/X×(10%-25%).

According to other embodiments of the invention, as shown in FIG. 5A-5C,after the via 210 has been formed completely through the nitride layer204, the method may further include conditioning the top surface 218 ofthe germanium layer 202 with a “conditioning” chemistry. The“conditioning” chemistry may correspond to the “third” chemistrydescribed in conjunction with FIG. 3A-3C above. The conditioningchemistry may cause the top surface 218 of the germanium layer 202 tohave primarily the same atomic termini.

FIG. 5A illustrates an enlarged view of the top surface 218 of thegermanium layer 202. After the via 210 has been formed, the top surface218 may consist of various types of atomic termini. For reference, thesetypes of termini are shown in FIG. 3A-3C as either hyride (“H”) orhydroxal (“OH”) termini. The amount and consistency of the H or OHtermini depends on how the germanium layer 202 was formed and on theenvironment and/or chemicals that the top surface 218 of the germaniumlayer 202 had been exposed to at any point during its formation, orduring subsequent processing, such as during the formation andpatterning of the overlying nitride layer 204. The H atomic terminirepresent hydride molecular endings that are attached, by molecularbonds, to the germanium (“Ge”) molecules comprising the material of thegermanium layer 202. The OH atomic termini represent hydroxal molecularendings attached, by molecular bonds, to the Ge molecules. The H and OHtermini therefore represent ligants of G-H molecules and G-OH molecules,repectively, as shown in FIG. 5A.

It would be desirable, however, in some circumstances, to have the topsurface 218 primarily consist of a single atomic termini (i.e., either Hor OH) depending on the composition of the material that will besubsequently formed atop the top surface 218. For example, certainmaterials may bond better to either H or OH termini, or may create amore natural transition between materials based on the atomiccharacteristics of either H or OH atomic termini. For example, hydridetermini have a low resistivity and therefore may be useful for makinggood contact with, or transitioning to, other low-resistive materials,such as metals or other conductive materials. On the other hand,hydroxyl termini have a high resistivity and may be useful for makinggood contact with, or transitioning to, dielectric materials.Furthermore, hydrides are hydrophobic while hydroxyls are hydrophilic.Therefore depending on the application, hydroxyls may be preferable tohydrides. For example, hydroxyls are useful for atomic layer deposition(ALD) processes such as used for the deposition of some high-kdielectric films. The ALD process is more beneficial when applied to ahydrophilic layer, as opposed to a hydrophobic layer when halideprecursors are used.

Therefore, referring to FIG. 5B, in one embodiment of the invention, aconditioning solution 220 may be applied to the top surface 218 of thegermanium layer 202 that causes the atomic termini to be convertedprimarily to hydride atomic termini. Conditioning solution 220 may be anaqueous solution of range 0.1%-2% hyrdrofluoric acid, optimized at 1%.In a like manner, as shown in FIG. 5C, if hyroxal atomic termini aredesired, a different conditioning solution 222 may be applied to thesurface of the germanium layer 202 that causes the atomic termini to beconverted primarily to OH termini. Conditioning solution 222 may be anaqueous solution of range 1%-29% ammonium hydroxide, optimized at 5%.

Several embodiments of the invention have thus been described. However,those ordinarily skilled in the art will recognize that the invention isnot limited to the embodiments described, but can be practiced withmodification and alteration within the spirit and scope of the appendedclaims that follow.

1-6. (canceled)
 7. A method, comprising: forming a germanium layer on asemiconductor substrate; the second chemistry is CH₂F₂/O₂/Ar, the thirdchemistry includes an O₂ plasma and a sulfuric acid mixture with anoxidizing agent.
 9. The method of claim 7, wherein the fourth chemistryis any one of vapor hydrofluorine (HF), vapor hydrochlorine (HCl),aqueous ultra-dilute HF, 1-29% ammonium hydroxide aqueous solution, or0.1-2% hydrofluoric acid.
 10. The method of claim 7, wherein wetcleaning of the germanium surface is performed at room temperature indilute 0.1-10% by volume concentrations for a brief period of time0.5-10 minutes.
 11. The method of claim 7, wherein the third etchremoves a portion of the oxide layer as the protective nitride buffer isbeing etched, hence the method also including forming the oxide layerthicker than necessary to compensate for removed portion.
 12. Anapparatus, comprising: a germanium layer on a substrate, the germaniumlayer having a surface with primarily the same atomic termin.
 13. Theapparatus of claim 12, wherein the surface has a primarily hydrophobicGe—H atomic termination.
 14. The apparatus of claim 13, furthercomprising a conductive material overlying the surface.
 15. Theapparatus of claim 12, wherein the surface has a primarily hydrophilicGe—OH atomic termination.
 16. The apparatus of claim 15, furthercomprising a dielectric material overlying the surface.
 17. Theapparatus of claim 12, further comprising: a nitride layer overlying thegermanium layer; and an oxide layer overlying the germanium layer.